Indirectly heated cathode of small filament current power



INDIRECTLY HEATED CATHODE OF SMALL FILAMENT CURRENT POWER Filed Sept. '29, 1960 July 27, 1965 F. H. R. ALMER ETAL 2 Sheets-Sheet 1 ENTOR FIG.

y 27, 1965 F. H. R. ALMER ETAL 3,197,667

INDIRECTLY HEATED CATHODE OF SMALL FILAMENT CURRENT POWER Filed Sept. 29, 1960 2 Sheets-Sheet 2 K AGENT E United States Patent 243,986 4 Claims. (Cl. 313-263) T he invention relates to an indirectly heated cathode requiring a filament current power of less than 1 watt and comprising an elongated cylindrical support thelongitudinal axis of which extends parallel to the active surface of the next electrode.

The known indirectly heated cathodes generally require a filament current power of from 2 to 4 watts and this is a serious disadvantage when such a cathode must be fed from batteries and especially if it is a cathode of a cathode-ray tube which must co-operate with transistors in portable television receivers or oscillographs. The comparatively prolonged warming-up time of from about 0.5 to 1 minute of the known cathodes also is a disadvantage.

It has now been found that the said disadvantages can be considerably reduced in an indirectly heated elongated cylindrical cathode the longitudinal axis of which extends parallel to the active surface of the next electrode if, in accordance with the invention, the cathode is secured to an insulated member by means of two parallel arranged strips which extend at right angles to the longitudinal axis of the cathodes and have about the same length as the cathode cylinder. The strips may be integral with the cathode cylinder and preferably at least one of the strips closes one end of the cathode cylinder. The cathode cylinder preferably comprises a bent or folded metal plate made of an alloy having great strength and also a comparatively poor thermal conductivity, for example nickel-iron, while a second cylinder made of nickel and carrying the emission layer may be slipped onto the first cylinder. It has been found that in this arrangement a filament current power of 0.5 watt is sufficient while the warm-up time of the cathode is only from 3 to 4 seconds. Furthermore, the differences in the temperatures of different cathodes prove to be very slight in this arrangement owing to the fact that the heat dissipation from the ends of the strips to the insulating member proves to be always the same.

The invention will now be described more fully with reference to a drawing in which:

FIGS. 1 and 3 are side elevations of a cathode in accordance with the invention for use in an electron gun, while FIG. 2 is a cross-sectional view and FIG. 4 a plan view of the embodiment shown in FIGS. 1 and 3.

In the figures, the cathode comprises a cylinder produced by folding a metal plate 1 and having a rectangular cross-sectional area. The cathode 1 is surrounded by a Wehnelt electrode or control grid 2. The cylinder 1 is supported by comparatively long narrow strips 3 and 4 extending parallel to one another at right angles to the direction of length of the cathode, which may be welded to the edges of the cylinder 1. Since these strips 3 and 4 are long, that is to say, about as long as the cathode, the heat dissipation is very small, especially since these strips 3 and 4 are made of a hard material, for example nickel-iron, of poor thermal conductivity. Because the material is hard, the cross-sectional area of .the strips 3 and 4 may be very small in spite of their great length,

the more so since reenforcing ribs 20 are pressed in these strips so that they have a great rigidity at a very slight thickness. The strip 4 is provided with a widened part 5 by which the cathode cylinder is closed at one end. Since the material of the cylinder is not very suitable as a base for the emission layer 12, a nickel cylinder 10 is slipped onto the cylinder 1, which cylinder 10 may be provided with a lug 11 acting to close this end of the cathode cylinder. The strips 3 and 4 may have a thickness of about 0.07 mm., and a length of about 6 mm. The length of the cylinder 1 may be about 3.5 mm., and the size of the usual bariumstrontium active oxide coating 12 on the nickel base 10 may be about 3 x 1 mm.

The cathode cylinder encloses a heater 13 the ends of which are connected in the form of insulated stretched wires 15 to current supply members 16. In the vicinity of the lug 11 the wire ends 15 are coated with insulating material 14. The members 16 are each provided with a current supply conductor 17. In order to prevent metal evaporating from the cathode from forminga conductive bridge between the support strips 3 and 4 and the Wehnelt cylinder 2, the insulating member to which the cathode is secured comprises three mica plates 6, 7 and 8, the plate 7 having a smaller diameter than the plate 6, whilethe Wehnelt cylinder is secured to the plate 8 by means of lugs 19. The mica plates 6, 7 and 8 are kept together by the strips 3 and 4 and a brace 9, which abuts the bottom mica plate 8 and which is welded at its bent ends to the projecting ends of the support strips 3 and 4. If desired, separate screens may be provided to prevent the occurrence of conducting leakage paths along the surface of the mica plate 6 between the filament supply members 16 and 17 and the strips 3 and 4. The entire gun may be secured in the usual manner to insulating stay rods by means of rods 18 welded to the Wehnelt cylinder.

The cylinder 1 may alternatively be made from nickel instead of from nickel-iron. The strips 3 and 4 may in this event be made from nickel-iron and be Welded to short lugs of the cylinder 1. Thus, the separate nickel outer jacket 10 may be omitted while the lug 11 may form part of the cylinder 1 and may also serve to secure the support strip 3.

Since the long strips 3 and 4 extend at right angles to the longitudinal axis of the cathode and parallel to one another, lateral shifting of the cathode, for example due to impact or in mounting, will cause the cathode to move along its longitudinal axis and parallel to the surface of the Wehnelt electrode, the distance by which it is spaced from the Wehnelt electrode remaining substantially constant owing to the fact that the ends of the strips 3 and 4 describe arcs of circles of large diameter, as is shown in FIG. 2 by curved arrows. Hence, such comparatively long strips 3 and 4 can be used, as is necessary for the small heat dissipation, without giving rise to difliculties due to distance variations. Displacement of the cathode is further restricted by the straight ends 15 of the filament. The distance by which the cathode is spaced from the surface of the Wehnelt cylinder 2 is scarcely influenced by mounting, since this spacing is accurately determined by widened parts 21 of the strips 3 and 4 bearing on the mica plate 6.

Although a single embodiment of the invention has been described, the invention may also be used in tubes of ditferent types, such as amplifier tubes, tuning indicator tubes and similar tubes which cannot be replaced by transistors.

What is claimed is:

1. In an electron discharge tube an electrode assembly comprising a cylindrical cathode having a given longitudinal axis, a heater element within said cathode, at least one other electrode having an active surface and surroundta ing said cathode, the active surface of said other electrode being parallel to the longitudinal axis of the Cathode, an insulating member spaced from said cathode, and a plurality of reinforced parallel cathode supporting strips of relatively poor thermal conductivity having about the same length as the cathode extending at right angles to the longitudinal axis of and securing the cathode to said insulating member, at least one end of said cathode being closed by one of said supporting strips.

2. In an electron discharge tube an electrode assembly comprising a cylindrical folded metal plate cathode having a given longitudinal axis, a heater element within said cylindrical cathode, at least one other electrode having an active surface and surrounding said cathode, the active surface of said other electrode being parallel to the longitudinal axis of the cathode, an insulating member spaced from and supporting said cathode, and a plurality of reinforced parallel cathode supporting strips of relatively poor thermal conductivity integral with the cathode and having about the same length as the cathode extending at right angles to the longitudinal axis of and securing the cathode to said insulating member, at least one end of said cathode being closed by one of said supporting strips.

3. In an electron discharge tube an electrode assembly comprising a cylindrical cathode having a given longi tudinal axis, a heater element within said cylindrical cathode, at least one other, electrode having an active surfaceand surrounding said cathode, the active surface of said other electrode being parallel to the longitudinal axis of the cathode, an insulating member spaced from and supporting said cathode, and a plurality of reinforced parallel cathode supporting strips of relatively poor thermal conductivity integral with the cathode and having about the same length as the cathode extending at right angles to the longitudinal axis of and securing the cathode to said insulating member, at least one end of said cathode cylinder being closed by one of said supporting strips.

4. In an electron discharge tube an electrode assembly comprising a cylindrical cathode having a given longitudinal axis, said cathode comprising a folded nickel-iron plate, a second metal cylinder supporting an emissive layer coaxial with and surrounding said folded plate, a heater element within said cylindrical cathode adapted to heat said cathode with a power input of less than 1 watt, at least one other electrode having an active surface and surrounding said cathode, the active surface of said other electrode being parallel to the longitudinal axis of the cathode, an insulating member spaced from and supporting said cathode, and a plurality of reinforced parallel cathode supporting strips of relatively poor thermal conductivity integral with the cathode and having about the same length as the cathode extending at right angles to the longitudinal axis of and securing the cathode to said insulating member, at least one end of said cathode cylinder being closed by one of said supporting strips.

References Cited by the Examiner UNITED STATES PATENTS 1,666,010 4/28 Hawadier 313-27O 2,227,599 1/41 McNaney 313-310 2,414,137 1/47 Branson 3 l3270 X 2,899,591 8/59 Stein 3l3337 DAVID J. GALVIN, Primary Examiner.

RALPH G. NILSON, ARTHUR GAUSS, JAMES D.

KALLAM, Examiners. 

1. IN AN ELECTRON DISCHARGE TUBE AN ELECTRODE ASSEMBLY COMPRISINGG A CYLINDRICAL CATHODE HAVING A GIVEN LONGITUDINAL AXIS, A HEATER ELEMENT WITHIN SAID CATHODE, AT LEAST ONE OTHER ELECTRODE HAVING AN ACTIVE SURFACE AND SURROUNDING SAID CATHODE, THE ACTIVE SURFACE OF SAID OTHER ELECTRODE BEING PARALLEL TO THE LONGITUDINAL AXIS OF THE CATHODE, AN INSULATING MEMBER SPACED FROM SAID CATHODE, AND A PLURALITY OF REINFORCED PARALLEL CATHODE SUPPORTING STRIPS OFF RELATIVELY POOR THERMAL CONDUCTIVITY HAVING ABOUT THE SAME LENGTH AS THE CATHODE EXTENDING AT RIGHT ANGLES TO THE LONGITUDINAL AXIS OF AND SECURING THE CATHODE TO SAID INSULATING MEMBER, AT LEAST ONE END OF SAID CATHODE BEING CLOSED BY ONE OF SAID SUPPORTING STRIPS. 